Following Big Jim's reign of terror in the drama's freshman season, the series from exec producers Stephen King, Steven Spielberg, Neal Baer and Brian K. Vaughan has given the show's big bad a new rival in Cahill. The actor is set to play Sam, Big Jim's (Dean Norris) brother-in-law. The character is described as a handsome recluse and former EMT who can hold his own against Big Jim and forms a deep connection with Julia (Rachelle Lefevre).

Cahill, repped by UTA and Management 360, was a series regular for all 197 episodes of CSI: NY, where he played Detective Don Flack. His credits also include romancing Jennifer Aniston's Rachel on Friends, Glory Days and an episode of Dawson's Creek.

Crome, meanwhile, will make her U.S. TV debut as Rebecca, a beautiful teacher who is athletic, smart, tough and sexy. She grew up as an Army brat and lived with her family in many locations around the world. The actress, whose credits include Hit & Miss opposite Chloe Sevigny as well as Misfits, Lightfields, Prisoners Wives and BAFTA-winning drama Murder, is repped by Troika and Thruline Entertainment.

The cast additions come as Under the Dome is poised to kill off two "favorites" when it returns with its King-penned season-two premiere June 30.

Vaughan told THR last year that the series will continue to focus on the human drama rather than the otherworldly beings introduced at season's end.

"Even though we've introduced these people behind the dome, we don't want it to become a show about us versus aliens. The dome is only there to pit us against each other and challenge our characters," he said. "We hope that will keep it a grounded human drama. We've always described the dome as a baby from another world and it's still learning to talk with us."